In order to meet the demand for wireless data traffic that is on an increasing trend after commercialization of 4G communication systems, efforts have been made to develop improved 5G or pre-5G communication system. For this reason, the 5G or pre-5G communication system is also called a beyond 4G network communication system or a post LTE system. In order to achieve high data rate, implementation of a 5G communication system in an ultrahigh frequency (mmWave) band (e.g., like 60 GHz band) has been considered.
In order to mitigate a path loss of radio waves and to increase a transfer distance of the radio waves in the ultrahigh frequency band, technologies of beamforming, massive MIMO, full dimension MIMO (FD-MIMO), array antennas, analog beamforming, and large scale antennas for the 5G communication system have been discussed. Further, for system network improvement in the 5G communication system, technology developments have been made for an evolved small cell, advanced small cell, cloud radio access network (cloud RAN), ultra-dense network, device to device communication (D2D), wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), and reception interference cancellation. In addition, in the 5G system, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC), which correspond to advanced coding modulation (ACM) systems, and filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA), which correspond to advanced connection technologies, have been developed.
On the other hand, the Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of things (IoT) where distributed entities, such as things, exchange and process information. The Internet of everything (IoE), which is a combination of the IoT technology and big data processing technology through connection with a cloud server, has emerged. As technology elements, such as sensing technology, wired/wireless communication and network infrastructure, service interface technology, and security technology, have been demanded for IoT implementation, a sensor network for machine-to-machine connection, machine-to-machine (M2M) communication, machine type communication (MTC), and so forth have been recently researched.
Such an IoT environment may provide intelligent Internet technology (IT) services that create a new value to human life by collecting and analyzing data generated among connected things. The IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between the existing information technology (IT) and various industries.
Accordingly, various attempts have been made to apply the 5G communication system to IoT networks. For example, technologies of sensor network, machine to machine (M2M) communication, and machine type communication (MTC) have been implemented by techniques for beam-forming, MIMO, and array antennas, which correspond to the 5G communication technology. As the big data processing technology as described above, application of a cloud radio access network (cloud RAN) would be an example of convergence between the 5G technology and the IoT technology.
On the other hand, in order to achieve evolution from the existing 4G LTE system into the 5G system, 3GPP that takes charge of the cellular mobile communication standard has named a new core network structure a 5G core (5GC) and has proceeded with the standardization thereof.
As compared with an evolved packet core (EPC) that is an existing 4G network core, the 5GC supports the following discriminated functions. The first is introduction of a network slice function. As the 5C requirements, the 5GC should support various types of terminals and services: e.g., enhanced mobile broadband (EMBB), ultra-reliable low latency communications (URLLC), and massive machine type communications (mMTC). Such terminals/services have different requirements used in respective core networks. For example, in case of an eMBB service, high data rate may be used, whereas in case of a URLLC service, high stability and low latency may be used.
A technology proposed to satisfy such various service requirements is a network slice scheme. Network slice is a method for virtualizing one physical network to make several logic networks, and respective network slice instances (NSIs) may have different characteristics. This becomes possible by making the respective NSIs have network functions (NF) that suit the characteristics. Several 5G services can be efficiently supported by allocating to terminals the NSIs that suit the characteristics of services used for the respective terminals.
The second may be easiness in network virtualization paradigm support through separation between a mobility management function and a session management function. In the existing 4G LTE, all terminals can be provided with services in a network through signaling exchange with single-core equipment that is called a mobility management entity (MME) taking charge of registration, authentication, mobility management, and session management functions. However, in the 5G, since the number of terminals is explosively increased, and mobility and traffic/session characteristics to be supported are subdivided in accordance with terminal types, scalability to add entities for necessary functions is lowered in case where all functions are supported by the single equipment such as the MME. Accordingly, in order to improve the scalability in function/implementation complexity of the core equipment taking charge of control plane and signaling load, various functions have been developed based on a structure for separating the mobility management function and the session management function from each other.
FIG. 1 illustrates a network architecture for a 5G system. An access and mobility management function (AMF) of managing terminal mobility and network registration and a session management function (SMF) of managing an end-to-end session are separated from each other, and may send and receive signaling through an N11 interface.
Third, a 5G terminal may set up a plurality of packet data unit (PDU) sessions for data communication with one data network name (DNN) such as Internet. Accordingly, the 5G terminal supports a function of making and removing UP connection (i.e., data radio bearer+N3 tunnel) between a terminal (UE) and a core network (CN) independently for respective PDU sessions.
Basically, if a terminal goes to a CM-IDLE state, it releases the UP connection of all PDU sessions. The terminal in the CM-IDLE state remakes only the UP connection of the PDU session to which mobile-originated (MO) or mobile-terminated (MT) traffics belong when returning again to a CM-CONNECTED state due to the mobile-originated (MO) or mobile-terminated (MT) traffics.
The terminal in the CM-CONNECTED state may perform an activation procedure of additionally making the UP connection with respect to the PDU session in which the UP connection has not yet been made. Further, the terminal in the CM-CONNECTED state can maintain only the UP connection of the PDU session in which the traffic occurs by performing a procedure of deactivating the UP connection of the activated PDU session through the network entity (e.g., AMF or SMF) of the core network, and thus UP connection resources can be saved. By independently activating the UP connection of the PDU session as described above, the signaling and UP connection resources can be additionally saved when the terminal performs a handover.